C# is close enough to Java that you should be able to learn it (assuming you know programming itself. If you don't, knowing just a language isn't going to do you much good.) You're not going to be able to "build" by drag & drop, though, you'll have to write code. (And not everything in Java is an object.) If you know programming, even a "learn Java in 21 days" or "learn Android programming in 21 days" book should be enough.